http://gcmd.nasa.gov/r/l/TermsOfUse9.1.52020-05-21 17:26:37OXYGENA colorless, odorless, gaseous element, constituting 21 percent of the
volume of the atmsophere, and essential for aerobic forms of life. Gaseous
oxygen has a chemical forumla of O2. Dissolved oxygen is included as a
detailed variable under Oxygen.